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Please Help Me With My Very Lazy Gt2860-9's!


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Hi all!

Thought I'd throw my question up here for all the experts out there. My story is that I've just had my brand new GT2860-9 turbos tuned on my R33 GTR only to find that they didn't meet any expectations. Infact, the car makes no more power than with the ceramics even though a massive amount of boost was dialed in!

The car made no more than 250kw / 340hp at 18 pounds although it has all the minimum upgrades that all the cars in the "dyno comparsion thread" have on here. http://www.skylinesa...l-dyno-results/

The average power that one is meant to achieve with -9's (or GT-SS turbos) is about 300kw/408hp with approx 18 pounds (that's taken from the spreadsheet in the above-mentioned thread)

The turbos made full boost by an excruciating late 5500-6000rpm which is absolutely shocking by any GT2860 standards. The throttle felt like it was made from rubber and all the prior ceramic turbo response is gone.....ie, full boost by no later than 4300 or so.

If any one could offer some feedback on past experiences with GT2860 turbos that would be great. Please don't rub in your figures tho - trust me, I've probably already read them in the comparisons / results thread ;)

Here are my basic mods:

Haltech E11v2 ecu tuned by Mercury

Bosch intank blah blah

Nismo 600cc squirters

Splitfire coils

Xforce split dumps with divider taken out because the -9s have their own

2.5" front pipes

3.5" main system with old cat (i'm suspicious of this and how much flow it's blocking)

Normal canon at rear

Pods

Adjustable cam gears (that they weren't able to do much with power gain wise)

If anyone could give me some feedback on what might be going on here that would be great. Please note that my car made about 330-350hp with the ceramic turbos on the same exhaust setup (minus injectors and cam gears) and also made 375hp with a set of used R33 N1 turbos. It's these past figures that make the new ones with the -9's seem so frustrating!

Edited by tommis85
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As u stated I rekon the Cat could be blocked or very very restrictive...

Yeh it probably is the culprit or one of them. But the spanner in the works is that my ceramics were venting into that very same system with the same cat and were maxing out ;) But then and again...ceramics can work well in a restrictive system being stock spec and all. Maybe the new turbos need to be totally free'd up?

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As u stated I rekon the Cat could be blocked or very very restrictive...

Yep - most logical place to start. If its not a metal matrix 100 or 200 cell already, just get one of those as it will be a worthwhile investment even if there are other problems. Check the flange sizes on your front pipe and catback to get something that either matches both, or matches the larger of the two. Some jap catback 3.5in systems use 3 in flange.

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My solid bet goes to the exhaust having an in-built restrictor somewhere that will be causing your issues.

It'll taper down to 2.5" or 2.25" somewhere near a muffler. You can usually tell from the outside where the step down occurs.

At 18psi the -9s, the motor is flowing a lot more air, and the enemy of forced induction is back pressure post turbo so stands to reason previous setup could well have been fine

Could also be the CAT as you've mentioned.

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Yeh it probably is the culprit or one of them. But the spanner in the works is that my ceramics were venting into that very same system with the same cat and were maxing out ;) But then and again...ceramics can work well in a restrictive system being stock spec and all. Maybe the new turbos need to be totally free'd up?

The -9s should just be a little bit laggier than the stockers (my -7s are) so say 16 psi at around 4000. You're right that since it was working ok with the current exhaust it doesn't sound like its the whole problem. Boost control setup properly? Any leaks? If you're REALLY careful you could disconnect the boost signal to the actuators and plug the hose, then take it up to around 4000 to see if its builds boost differently. If it builds a lot better then your boost control needs work.

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Thanks guys, looks like we all agree where I need to start.

Mr Stabby - yep, I'll get it booked in ASAP because for all that I know that thing could be completely blocked up (judging by all the crap that I wash of the rear of the car)

Nismoid - yes it must be something like that. The most narrow part of the exhaust would be inside the straight-thru canon though...everything else should be ok (apart from cat) although the system does have some unnecessary bends in it.

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Yeh from what I know the -9's shouldn't be too much later than the -7s (which I nearly ended up buying btw). However, there's quite a big difference with 16psi by 4000 and maybe what, 8-10psi by 4000? :D Shocking!

I could check the actuators however I'm running very firm ones - they should be at least 1 bar from memory. They're definitely not cracking open prematurely..

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Bends wont be a problem really in most instances... The jap exhausts a lot of the time have plates welded into their "3.5" exhausts from the production line. It's hard to tell from the outside, and sometimes you can't even see them without taking them off and having a good inspection.

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Bends wont be a problem really in most instances... The jap exhausts a lot of the time have plates welded into their "3.5" exhausts from the production line. It's hard to tell from the outside, and sometimes you can't even see them without taking them off and having a good inspection.

Ah ok fair enough...well mines a locally made 3.5" mild steel job. I sure hope they didn't weld any restrictors into it!

Also, while we're talking restrictions - I do believe that the intake of the cat could be smaller than it's exit...what Mr Stabby was referring to.

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Haha no worries...well, first order of business will be to replace the cat then. Second order of business would probably be a larger cannon muffler that matches at least the internal dia of the piping. Those two things should really help improve the situation!

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First thing first......are you sure they are indeed -9s? :ermm:

Also did you test the acts before using a compressed air source to make sure they are opening at the same time and at what psi?

And as suggested before you can remove the feed to the acts and take it up to about 4k in 3rd or 4th with some one watching the boost gauge to see how much it makes......when i did this on mine, it showed that they were definitely capable of 18-20psi at around 4k

What are you using for boost control?

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Who did the turbo install? perhaps you have restrictive (OEM) gaskets, like a 2.5" (inner diameter) gasket between the front pipe and cat, or something small between the turbo and dump pipe, or dump pipe and front pipe etc

Is the fuel pump running at alternator voltage?

Were the actuators new (or were the factory 8psi ones re-used?), also are they adjustable? Maybe 1 turbo is doing all the work while the other isn't doing much (more preload on the actuator than the other).

Was the timing rechecked when the adjustable gears went on?

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Don Dana makes a good point, are they actually "GT2860-9's" because if so, that model are actually disco potatoes. GT2859-9's are the ones that are equivalent to the factory ceramics

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Haha yeh guys stop scaring the &^%$ out of me!

The ones I got are the direct bolt ons with part number 707160-5009 and I got them with 15.6 pound actuators (and they sure feel like it but should probably test their psi).

Regarding the timing - I'm thinking that Mercury would have checked all this ;) Hopefully...

I've done all my turbo installs myself and all the gaskets match the pipe inner diameters.

However, I do have one question for you guys - what's the general consensus on split dump pipes? I'm using a set of x-force ones....and I'm about as suss of those as I am of my apparently clogged up cat. It would be nice to see exactly what sort of airflow happens inside those pipes - I bet it's turbulent as fark lol.

....ah the long process of ruling things out ;)

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The splitter in split dump pipes can foul on the wastegate flap (big problem with cheap ones on RB25DETs), the split itself is just too short to be of any benefit anyway, also of note the x-force design is just a copy of the HKS design. They shouldn't have a problem flowing 350kw+ though.

If the cat has 2.5" ends, then I wouldn't be surprised if power was restricted to 250kw. For your power level you want at least 3" ends, 3.5" ideally to match the cat back.

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Gents, thanks for the replies ;)

I've been doing some more reflecting and have remembered another little detail that would back up the excessive back-pressure theory:

When I drive off, it is very quick to make about 4-5psi before it just goes spongy and boost level creeps up with RPM. I'm thinking that this would be because of how the back pressure builds up in the front pipes / front portion of exhaust before the cat etc. There's enough flow to ramp the turbos up quickly to that 4-5psi and then they have to start pushing fumes down the exhaust harder and harder.

It would seem to me that so far it's only the ceramic turbos that have been able to survive in this high backpressure environment because they don't need much flow to make boost. I mean hell, they were able to make 14 pounds with the stock exhaust system haha.

Really hoping this theory is right :unsure:

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